Re: [PATCH 1/2] exec: make argv/envp memory visible to oom-killer

[KOSAKI Motohiro]

> Brad Spengler published a local memory-allocation DoS that
> evades the OOM-killer (though not the virtual memory RLIMIT):
> http://www.grsecurity.net/~spender/64bit_dos.c
> 
> execve()->copy_strings() can allocate a lot of memory, but
> this is not visible to oom-killer, nobody can see the nascent
> bprm->mm and take it into account.
> 
> With this patch get_arg_page() increments current's MM_ANONPAGES
> counter every time we allocate the new page for argv/envp. When
> do_execve() succeds or fails, we change this counter back.
> 
> Technically this is not 100% correct, we can't know if the new
> page is swapped out and turn MM_ANONPAGES into MM_SWAPENTS, but
> I don't think this really matters and everything becomes correct
> once exec changes ->mm or fails.
> 
> Reported-by: Brad Spengler <spender@xxxxxxxxxxxxxx>
> By-discussion-with: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
> Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>

Looks good to me.
	Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>


Thank you very much.


> --- K/fs/exec.c~acct_exec_mem	2010-11-30 18:27:15.000000000 +0100
> +++ K/fs/exec.c	2010-11-30 18:28:54.000000000 +0100
> @@ -164,6 +164,25 @@ out:
>  
>  #ifdef CONFIG_MMU
>  
> +static void acct_arg_size(struct linux_binprm *bprm, unsigned long pages)

One minor request.

I guess this function can easily makes confusing to a code reader. So I
hope you write small function comments. describe to
 - What is oom nascent issue
 - Why we think inaccurate account is ok


> +{
> +	struct mm_struct *mm = current->mm;
> +	long diff = (long)(pages - bprm->vma_pages);
> +
> +	if (!mm || !diff)
> +		return;
> +
> +	bprm->vma_pages = pages;
> +
> +#ifdef SPLIT_RSS_COUNTING
> +	add_mm_counter(mm, MM_ANONPAGES, diff);
> +#else
> +	spin_lock(&mm->page_table_lock);
> +	add_mm_counter(mm, MM_ANONPAGES, diff);
> +	spin_unlock(&mm->page_table_lock);
> +#endif
> +}
> +




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